Abstract:

A method for determining conditions for forming a dielectric SiOCH film,
includes: (i) forming a dielectric SiOCH film on a substrate under
conditions; (ii) evaluating the conditions using a ratio of Si--CH3
bonding strength to Si--O bonding strength of the film as formed in step
(i); (iii) if the ratio is 2.50 % or higher, confirming the conditions,
and if the ratio is less than 2.50 %, changing the conditions by changing
at least one of the susceptor temperature, the distance between upper and
lower electrodes, the RF power, and the curing time; and (iv) repeating
steps (i) to (iii) until the ratio is 2.50 % or higher.

Claims:

1. A method for determining conditions for forming a dielectric SiOCH
film, comprising:(i) forming a dielectric SiOCH film on a substrate under
conditions including a susceptor temperature, a distance between upper
and lower electrodes, an RF power, and a curing time;(ii) evaluating the
conditions using a ratio of Si--CH3 bonding strength to Si--O bonding
strength of the film as formed in step (i);(iii) if the ratio is 2.50% or
higher, confirming the conditions, and if the ratio is less than 2.50%,
changing the conditions by changing at least one of the susceptor
temperature, the distance between upper and lower electrodes, the RF
power, and the curing time; and(iv) repeating steps (i) to (iii) until
the ratio is 2.50% or higher.

2. The method according to claim 1, wherein the film as formed in step (i)
has a dielectric condition (k) and an elastic modulus (EM) which satisfy
2.4<k<2.6 and 8 GPa<EM.

3. The method according to claim 1, wherein the ratio is determined based
on an FT-IR spectrum of the film.

4. The method according to claim 1, wherein step (iii) comprises, if the
ratio is less than 2.50%, reducing the susceptor temperature, increasing
the distance between the upper and lower electrodes, decreasing the RF
power, and/or shortening the curing time.

5. The method according to claim 1, wherein the curing time is a time of
UV curing.

6. The method according to claim 1, wherein step (i) comprises:introducing
a silicon-containing hydrocarbon gas having a crosslinkable group, a
porogen gas, an oxidizing gas, and an inert gas into a reaction chamber
wherein the substrate is placed on the susceptor;applying RF power to the
reaction chamber between the upper and lower electrodes to generate a
plasma reaction region in the reaction chamber, thereby depositing a thin
film on a substrate; andcuring the thin film until a dielectric condition
(k) and an elastic modulus (EM) of the film satisfy 2.4<k<2.6 and 8
GPa<EM.

7. The method according to claim 1, wherein in step (iii), under the
confirmed conditions, a decrease of thickness of the film and an increase
of dielectric constant of the film are less than 3% and less than 0.25,
respectively, before and after the curing.

8. A method for forming a dielectric SiOCH film on a substrate,
comprising:confirming the conditions for forming a dielectric SiOCH film
according to claim 1; andforming a dielectric SiOCH film on a substrate
under the conditions.

9. The method according to claim 8, wherein the curing is UV curing.

10. The method according to claim 8, wherein the forming step
comprises:introducing a silicon-containing hydrocarbon gas having a
crosslinkable group, a porogen gas, an oxidizing gas, and an inert gas
into a reaction chamber wherein the substrate is placed on the
susceptor;applying RF power to the reaction chamber between the upper and
lower electrodes to generate a plasma reaction region in the reaction
chamber, thereby depositing a thin film on a substrate; andcuring the
thin film until a dielectric condition (k) and an elastic modulus (EM) of
the film satisfy 2.3<k<2.8 and 5 GPa<EM.

11. The method according to claim 8, wherein a decrease of thickness of
the film and an increase of dielectric constant of the film are less than
3% and less than 0.25, respectively, before and after the curing.

12. The method according to claim 10, wherein the silicon-containing
hydrocarbon gas is at least one selected from the group consisting of
silicon-containing hydrocarbon gases having alkoxyl group and/or vinyl
group as the crosslinkable group.

13. The method according to claim 10, wherein the porogen gas is at least
one selected from the group consisting of hydrocarbon gases of linear or
cyclic CnHm wherein n is an integer of 4-14 and m is an integer of 4-30.

14. The method according to claim 13, wherein the porogen gas is at least
one selected from the group consisting of α-terpinene,
β-terpinene, γ-terpinene, hexane, and cyclohexane.

15. The method according to claim 10, wherein the oxidizing gas is at
least one selected from the group consisting of )2 and N2O.

16. The method according to claim 10, wherein the inert gas is at least
one selected from the group consisting of He, Ar, Kr, and Xe.

17. The method according to claim 10, wherein the curing is conducted by
UV light for a time period of less than 700 seconds.

18. A method for forming an interconnect structure on a substrate,
comprising:forming a dielectric SiOCH film on a substrate according to
claim 10; andforming an interconnect structure on the substrate by single
or dual damascene.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention generally refers to a semiconductor
technology. In particular, it relates to a method for forming on a
semiconductor substrate a silicon-containing insulation film having high
chemical stability and low dielectric constant by using a plasma CVD
(chemical vapor deposition) apparatus.

[0003]2. Description of the Related Art

[0004]The demand for semiconductors offering higher processing speeds and
smaller circuits in recent years is giving rise to a need to reduce
wiring resistances and inter-wiring volumes to prevent signal delays in
multi-layer wiring structures.

[0005]To reduce wiring resistances, wirings that use copper as the main
conductor material are being examined. To form copper wirings, the
so-called damascene structure is used wherein a wiring metal that uses
copper as the main conductor material is deposited on a substrate,
including inside grooves formed in an insulation film, after which
excessive wiring metal in areas outside the grooves is removed by the CMP
method to form a wiring pattern in the grooves. With the damascene
structure, a wiring metal is deposited on a substrate, including the
inside grooves, after which excessive wiring metal in areas outside the
grooves is removed by the CMP method to form wirings inside the grooves.
Damascene structures are largely divided into single damascene and dual
damascene structures. A single damascene structure is formed, for
example, by the following procedure: (1) Deposit an insulation film and
cure the film; (2) Form trenches in the insulation film; (3) deposit a
wiring metal on the insulation film and also inside the trenches; and (4)
grind the wiring metal layer via CMP so that the metal remains only
inside the trench. This way, embedded wirings can be formed inside the
trenches. A dual damascene structure is formed, for example, by the
following procedure: (1) Deposit an insulation film and cure the film;
(2) form trenches, as well as via holes in the insulation film for
connection with the bottom wiring layer; (3) deposit a wiring metal layer
on this insulation film and also inside the trenches and via holes; and
(4) grind the wiring metal layer via CMP so that the metal remains only
inside the trenches and via holes. This way, embedded wirings can be
formed inside the trench and via holes. There are mainly two ways to form
a dual damascene structure, including [1] the method to form trenches
first, and [2] the method to form via holes first. Of the two methods,
[2] involves a simpler process and is therefore used more widely.

[0006]In either of the structures described above, the inter-layer
insulation films are etched using hard mask, photoresist or other masking
material as deemed appropriate, after which ashing is performed. However,
it is impossible to remove all residues, and thus wet etching must be
performed using a chemical solution. If an insulation film of low
dielectric constant is used for inter-layer films, this wet etching
presents problems such as increase in dielectric constant and decrease in
film thickness. U.S. Pat. No. 6,846,515 describes a method for forming an
insulation film of low dielectric constant by forming voids in film
through a curing process using porogen gas. However, this method cannot
solve the aforementioned problems in practical applications involving
semiconductor devices.

[0007]To reduce inter-wiring volumes, the dielectric constants of
insulation films between multiple wiring layers must be lowered, and
therefore insulation films of low dielectric constants have been
developed for this purpose.

[0008]Traditionally a silicon oxide film SiOx is formed by adding oxygen
O2 as an oxidizing agent, as well as nitrogen oxide NO or nitrous oxide
N2O, to SiH4, Si(OC2 H5)4 or other silicon material gas, and then
processing the mixture by means of heat or plasma energy. Silicone oxide
films thus formed have a dielectric constant E of approx. 4.0. On the
other hand, the spin coat method that uses inorganic silicon oxide glass
(SOG) as a material forms insulation films having a low dielectric
constant ε of approx. 2.3. Also, the plasma CVD method that uses
CxFyHz as the material gas forms fluorinated amorphous carbon films
having a low dielectric constant ε in a range of 2.0 to 2.4. In
addition, the plasma CVD method that uses a silicon-containing
hydrocarbon (such as P-TMOS (phenyl trimethoxysilane)) as the material
gas forms insulation films having a low dielectric constant ε of
approx. 3.1. Furthermore, the plasma CVD method that uses a
silicon-containing hydrocarbon having multiple alkoxy groups as the
material gas, forms insulation films having a low dielectric constant
ε of approx. 2.5 through optimization of conditions.

[0009]However, the aforementioned traditional approaches present problems
as described below. First, inorganic SOG insulation films formed by the
spin coat method present problems in that the material is not evenly
distributed over the silicon substrate and that the apparatus used in the
curing process after coating of material is expensive. Also, fluorinated
amorphous carbon films formed by the plasma CVD method using CxFyHz as
the material gas have drawbacks including low heat resistance of the film
(370° C. or below), poor adhesion property with respect to silicon
materials, and low mechanical strength of the film. If P-TMOS having
three alkoxy groups is used among silicon-containing hydrocarbons, the
polymerized oligomer cannot form a linear structure like that of
siloxane. As a result, a porous structure is not formed on the silicon
substrate and the dielectric constant cannot be lowered to a desired
level. If other silicon-containing hydrocarbon having multiple alkoxy
groups is used as the material gas, the polymerized oligomer obtained
under optimized conditions forms a linear structure like that of
siloxane, which allows for formation of a porous structure on the silicon
substrate and lowering of the dielectric constant to a desired level.
However, this oligomer having a linear structure provides weak
inter-oligomer bonding strength, thus resulting in low mechanical
strength of the film.

SUMMARY OF THE INVENTION

[0010]From the aforementioned viewpoints, a technology to form a damascene
structure by adopting a porous insulation film of low dielectric constant
(SiOCH film) for inter-layer films is being examined. However, the
technical problems mentioned above are not solved yet. To be specific,
with a damascene structure the inter-layer insulation films are etched
using hard mask, photoresist or other masking material as deemed
appropriate, after which ashing is performed. However, it is impossible
to remove all residues, and thus wet etching must be performed using a
chemical solution. If a porous insulation film of low dielectric constant
(SiOCH film) is used for inter-layer films, this wet etching tends to
present problems such as increase in dielectric constant and decrease in
film thickness.

[0011]The present invention was developed to address the aforementioned
problems, and aims to provide a method for forming a silicon-containing
insulation film having high chemical stability and low dielectric
constant.

[0012]Another object of the present invention is to provide a method for
forming an insulation film of low dielectric constant in an easy manner
without increasing the apparatus cost.

[0013]To solve at least one of the aforementioned problems, in an
embodiment of the present invention the method for forming low dielectric
constant film consists of the steps described below. To be specific this
method for forming a SiOCH low dielectric constant film as insulation
films between wiring layers is characterized in that the ratio of
strength of Si--CH3 bond and Si--O bond in the SiOCH film is 2.50% or
more.

[0014]In an embodiment of the present invention, the method for forming an
insulation film of low dielectric constant using the plasma CVD method
consists of: (a) a step to introduce into a reaction chamber a set of
material gases including a silicon-containing hydrocarbon that contains
multiplecrosslinkable groups such as alkoxy groups and/or vinyl groups, a
porogen gas, an oxidizing gas, and an inert gas; (b) a step to apply
first RF power and second RF power to generate a plasma reaction field in
the reaction chamber, or apply only the first RF power; and (c) a step to
optimize the flow rate of each material gas and the output of each RF
power.

[0015]Among the material gases, the silicon-containing hydrocarbon having
multiple crosslinkable groups consists of one silicon-containing
hydrocarbon having one or more crosslinkable groups or a combination of
such silicon-containing hydrocarbons. The porogen gas is a hydrocarbon
having a linear or cyclic structure expressed by the general formula
CnHm, where n is selected from the group consisting of numbers 4 to 14,
while m is selected from the group consisting of numbers 4 to 30,
respectively. Specifically, the porogen is selected from the group
consisting of α-terpinene, β-terpinene, γ-terpinene,
hexane and cyclohexane. The oxidizing gas is selected from the group
consisting of O2 and N2O. The inert gas is He, Ar, Kr or Xe or any
combination thereof. Since each of these gases has a different ionization
energy and collision cross-section area, the reaction in the vapor phase
can be controlled by changing the combination of these gases.

[0016]For purposes of summarizing the invention and the advantages
achieved over the related art, certain objects and advantages of the
invention are described in this disclosure. Of course, it is to be
understood that not necessarily all such objects or advantages may be
achieved in accordance with any particular embodiment of the invention.
Thus, for example, those skilled in the art will recognize that the
invention may be embodied or carried out in a manner that achieves or
optimizes one advantage or group of advantages as taught herein without
necessarily achieving other objects or advantages as may be taught or
suggested herein.

[0017]Further aspects, features and advantages of this invention will
become apparent from the detailed description of the preferred
embodiments which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]These and other features of this invention will now be described
with reference to the drawings of preferred embodiments which are
intended to illustrate and not to limit the invention. The drawings are
oversimplified for illustrative purposes and are not to scale.

[0019]FIG. 1 is a schematic diagram of a plasma CVD apparatus usable in an
embodiment of the present invention.

[0020]FIG. 2A is a FT-IR spectrum of a SiOCH film obtained in an
embodiment of the present invention. FIG. 2B is an enlarged partial FT-IR
spectrum of FIG. 2A showing an area of Si--CH3 and an area of Si--O for
calculating an area ratio.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021]The present invention will be explained in detail with reference to
preferred embodiments. However, the preferred embodiments are not
intended to limit the present invention.

[0022]In an embodiment, the present invention provides a method for
determining conditions for forming a dielectric SiOCH film, comprising:
(i) forming a dielectric SiOCH film on a substrate under conditions
including a susceptor temperature, a distance between upper and lower
electrodes, an RF power, and a curing time; (ii) evaluating the
conditions using a ratio of S---CH3 bonding strength to Si--O bonding
strength of the film as formed in step (i); (iii) if the ratio is 2.50%
or higher, confirming the conditions, and if the ratio is less than
2.50%, changing the conditions by changing at least one of the susceptor
temperature, the distance between upper and lower electrodes, the RF
power, and the curing time; and (iv) repeating steps (i) to (iii) until
the ratio is 2.50% or higher (including 2.6%, 2.8%, 3.0%, 3.2%, 3.5%, and
values between any two numbers of the foregoing, preferably 2.5% to
3.2%). The ratio may be determined based on an FT-IR spectrum of the
film, although any suitable method can be employed. By the above method,
the conditions for forming a dielectric SiOCH film can effectively be
determined, which film is suitable for damascene processes because a
dielectric constant and a thickness of the film do not change
significantly before and after curing.

[0023]The above embodiment further includes, but is not limited to, the
following embodiments:

[0024]In an embodiment, the film as formed in step (i) may have a
dielectric condition (k) and an elastic modulus (EM) which satisfy
2.3<k<2.8 and 5 GPa<EM, preferably 2.4<k<2.6 and 8
GPa<EM. In an embodiment, the dielectric constant of the film may be
in a range of 1.1 g/cm3 to 1.5 g/cm3.

[0025]In any of the foregoing embodiments, step (iii) may comprise, if the
ratio is less than 2.50%, reducing the susceptor temperature, increasing
the distance between the upper and lower electrodes, decreasing the RF
power, and/or shortening the curing time. In any of the foregoing
embodiments, the curing time may be a time of UV curing.

[0026]In any of the foregoing embodiments, step (i) may comprise: (a)
introducing a silicon-containing hydrocarbon gas having a crosslinkable
group, a porogen gas, an oxidizing gas, and an inert gas into a reaction
chamber wherein the substrate is placed on the susceptor; (b) applying RF
power to the reaction chamber between the upper and lower electrodes to
generate a plasma reaction region in the reaction chamber, thereby
depositing a thin film on a substrate; and (c) curing the thin film until
a dielectric condition (k) and an elastic modulus (EM) of the film
satisfy 2.3<k<2.8 and 5 GPa<EM, preferably 2.4<k<2.6 and 8
GPa<EM.

[0027]In any of the foregoing embodiments, in step (iii), under the
confirmed conditions, a decrease of thickness of the film and an increase
of dielectric constant of the film may be less than 3% (including 2.5%,
2%, 1.5%, 1%, 0.5%, and values between any two numbers of the foregoing)
and less than 0.25 (including 0.2, 0.15, 0.1, 0.05, and values between
any two numbers of the foregoing), respectively, before and after the
curing.

[0028]In another aspect, the present invention provides a method for
forming a dielectric SiOCH film on a substrate, comprising: (I)
confirming the conditions for forming a dielectric SiOCH film according
to any of the foregoing determination methods; and (II) forming a
dielectric SiOCH film on a substrate under the conditions.

[0029]The above embodiment further includes, but is not limited to, the
following embodiments:

[0030]In an embodiment, the curing may be UV curing.

[0031]In any of the foregoing embodiments, the forming step may comprise:
(A) introducing a silicon-containing hydrocarbon gas having a
crosslinkable group, a porogen gas, an oxidizing gas, and an inert gas
into a reaction chamber wherein the substrate is placed on the susceptor;
(B) applying RF power to the reaction chamber between the upper and lower
electrodes to generate a plasma reaction region in the reaction chamber,
thereby depositing a thin film on a substrate; and (C) curing the thin
film until a dielectric condition (k) and an elastic modulus (EM) of the
film satisfy 2.3<k<2.8 and 5 GPa<EM, preferably 2.4<k<2.6
and 8 GPa<EM. The decrease of thickness of the film and the increase
of dielectric constant of the film are described above.

[0032]In any of the foregoing embodiments, the silicon-containing
hydrocarbon gas may be at least one selected from the group consisting of
silicon-containing hydrocarbon gases having alkoxyl group and/or vinyl
group as the crosslinkable group. In any of the foregoing embodiments,
the porogen gas may be at least one selected from the group consisting of
hydrocarbon gases of linear or cyclic CnHm wherein n is an integer of
4-14 and m is an integer of 4-30. Further, the porogen gas may be at
least one selected from the group consisting of α-terpinene,
β-terpinene, γ-terpinene, hexane, and cyclohexane. In any of
the foregoing embodiments, the oxidizing gas may be at least one selected
from the group consisting of O2 and N2O. In any of the foregoing
embodiments, the inert gas may be at least one selected from the group
consisting of He, Ar, Kr, and Xe. In any of the foregoing embodiments,
the curing may be conducted by UV light for a time period of less than
700 seconds (including 500 sec., 300 sec., 100 sec., and values between
any two numbers of the foregoing; in other embodiments, 300-3600 sec.)
under curing conditions of 90 mW/cm2 of UV high pressure mercury lamp at
400° C., for example.

[0033]In still another aspect, the present invention provides a method for
forming an interconnect structure on a substrate, comprising: (1) forming
a dielectric SiOCH film on a substrate according to any of the foregoing
forming methods; and (2) forming an interconnect structure on the
substrate by single or dual damascene.

[0034]In yet another aspect, the present invention provides the following
embodimens:

[0035]1) A method for forming an insulation film on a substrate,
characterized in that the ratio of strength of Si--CH3 bond and Si--O
bond in the SiOCH film is 2.50% or more according to FT-IR.

[0036]2) A method for forming low dielectric film according to 1) above,
characterized in that the ratio of strength of Si--CH3 bond and Si--O
bond in the SiOCH film is in a range of 2.50% to 3.20%.

[0037]3) A method for forming low dielectric film according to 1) or 2)
above, characterized in that the dielectric constant of the SiOCH film is
2.6 or less.

[0038]4) A method for forming low dielectric film according to any one of
1) to 3) above, characterized in that the elastic modulus of the SiOCH
film is 8 GPa or more.

[0039]5) A method for forming low dielectric film according to any one of
1) to 4) above, characterized in that the SiOCH film is formed by the
plasma CVD method.

[0040]6) A method for forming low dielectric film according to 5) above,
wherein such method forms the film on a substrate through: (a) a step to
introduced into a reaction chamber in which a substrate is placed a set
of reactant gases including (A) a material gas constituted by a
silicon-containing hydrocarbon having multiple crosslinkable gas, (B) a
porogen gas, (C) an oxidizing gas, and (D) an inert gas; (b) a step to
apply RF power to form a plasma reaction field in the reaction chamber;
(c) a step to deposit a film by controlling the flow rates of reactant
gases and the intensity of RF power; and (d) a curing step to form voids
in the film.

[0041]7) A method according to 6) above, wherein the crosslinkable groups
constituting the silicon-containing hydrocarbon are alkoxy and/or vinyl
groups.

[0042]8) A method according to 6) or 7) above, wherein the porogen gas is
a hydrocarbon having a linear or cyclic structure expressed by the
general formula CnHm, where n is selected from the group consisting of
numbers 4 to 14, while m is selected from the group consisting of numbers
4 to 30, respectively.

[0043]9) A method according to any one of 6) to 8) above, wherein the
porogen gas is at least one selected from the group consisting of
α-terpinene, β-terpinene, γ-terpinene, hexane and
cyclohexane.

[0044]10) A method according to 7) above, wherein the material gas is a
chemical substance expressed by the chemical formula
Si.sub.αO.sub.α-1R2-β+2(OCnH2n+1).sub..be-
ta., where α is an integer of 1 to 3, β is 2 or 3, n is an
integer of 1 to 3, and R is bonded with Si and selected from the group
consisting of C1-2 hydrocarbons, C1-2 fluorocarbons, C1-2
perfluorocarbons, H, D, F, Cl, Brand I.

[0045]11) A method according to 10) above, wherein α is 1 or 2, and
β is 2.

[0046]12) A method according to 7) above, wherein the material gas is
diethoxy methylsilane.

[0047]13) A method according to 10) above, wherein R is one of C1-6
hydrocarbons.

[0048]14) A method according to 7) above, wherein the material gas is
dimethyl dimethoxysilane.

[0049]15) A method according to 7) above, wherein the material gas is
1,3-dimethoxy tetramethyl disiloxane.

[0050]16) A method according to 7) above, wherein the material gas is
1,3-divinyl tetramethyl disiloxane.

[0051]17) A method according to any one of 5) to 16) above, wherein the RF
power has a single frequency.

[0052]18) A method according to 17) above, wherein the frequency is 2 MHz
or more.

[0053]19) A method according to 18) above, wherein the frequency is 10 to
30 MHz.

[0054]20) A method according to any one of 6) to 19) above, wherein the
inert gas is selected from the group consisting of Kr, Xe, Ar, Ne and He.

[0055]21) A method according to any one of 6) to 20) above, wherein the
oxidizing gas is selected from the group consisting of )2 and N2O.

[0056]22) A method according to any one of 6) to 21) above, wherein the
intensity of RF power is 0.5 W/cm2 to 2.0 W/cm2 (or 0.7 W/cm2 to 1.5
W/cm2).

[0057]23) A method according to any one of 6) to 22) above, wherein the
inert gas is supplied at a flow rate of 5 to 30 times (or 10 to 20 times)
the flow rate of the material gas.

[0058]24) A method according to any one of 6) to 23) above, wherein the
curing process is implemented by means of thermal annealing, UV light or
electron beam.

[0059]25) A method according to any one of 6) to 24) above, wherein the
curing process is implemented at a temperature of 0 to 550° C. (or
100 to 450° C.) (normally a temperature of approx. 400° C.
is used).

[0060]The present invention will be explained in detail with reference to
the drawings and examples. However, the drawings and examples are not
intended to limit the present invention.

[0061]An apparatus configuration that can be used in the examples of the
present invention is described below, along with how it is used, and the
resulting improvements are explained.

[0062]In the present disclosure where conditions and/or structures are not
specified, the skilled artisan in the art can readily provide such
conditions and/or structures, in view of the present disclosure, as a
matter of routine experimentation. Also, in the present disclosure, the
numerical numbers applied in embodiments can be modified by ±50% in
other embodiments, and the ranges applied in embodiments may include or
exclude the endpoints.

[0063]FIG. 1 is a schematic diagram of a plasma processing apparatus used
in an embodiment of the present invention. This plasma processing
apparatus 1 comprises a reaction chamber 6, gas introduction port 5,
susceptor 3 and heater 2, and includes a second electrode. Gases are
introduced from the gas introduction port 5 through a gas line (not
illustrated). A circular first electrode 9 is positioned just below the
gas introduction port 5, where the first electrode 9 has a hollow
structure having many small holes in the bottom face through which gases
are injected onto a processing target 4. The first electrode 9 is also
structured in such a way that a shower plate 11 having multiple gas
introduction holes can be replaced for easy maintenance and reduction of
part costs.

[0064]Also, an exhaust port 10 is provided at the bottom of the reaction
chamber 6. This exhaust port 10 is connected to an external vacuum pump
(not illustrated) to exhaust the interior of the reaction chamber 6. The
susceptor 3 is positioned in parallel with and facing the first electrode
9. The susceptor 3 retains the processing target 4 on top, continuously
heats the processing target 4 by means of a heater 2, and thus maintains
the substrate 4 at a specified temperature (0 to 500° C.). The gas
introduction port 5 and first electrode 9 are insulated from the reaction
chamber 6 and connected to a first RF power supply 7 provided externally.
A second RF power supply 8 may be connected. 12 indicates ground. As a
result, the first electrode 9 and second electrode function as
high-frequency electrodes and generate a plasma reaction field near the
processing target 4. The type and quality of the film formed on the
surface of the processing target 4 vary according to the type and flow
rate of the material gas, temperature, RF frequency type, as well as
spatial distribution and potential distribution of plasma.

[0065]In an embodiment, chemical stability of the semiconductor device
structure is evaluated by a blanket film acceleration test.

[0066]For your reference, a buffered fluorinated acid (HF:NH4F=1:30) is an
example of the chemical agent used in this test. Although this buffered
fluorinated acid is sometimes considered a mixture of hydrofluoric acid
and ammonium fluoride, the hydrofluoric acid in the composition
immediately changes to monohydrate ammonium difluoride once mixed.
Accordingly, the buffered fluorinated acid is considered as a mixture of
5 g of monohydrate ammonium difluoride and 37 g of ammonium fluoride
hereunder. The etching rate with respect to the thermal oxide film is
approx. 700 Å .min if a buffered fluorinated acid of HF:NH4F=1:10 is
used.

[0067]The acceleration test procedure used to evaluate the chemical
stability of a blanket film is explained below.

[0068][1] As a pre-measurement step, measure the thickness, dielectric
constant (k) and FT-IR of the blanket film at one point at the center.

[0069][2] Soak the film for 40 seconds in a water bath containing a
buffered fluorinated acid mixed at a ratio of 1:30.

[0070][3] Rinse the film for 30 minutes twice in a water bath containing
pure water.

[0071][4] Dry the film using nitrogen gas, and immediately measure the
thickness, dielectric constant (k) and FT-IR of the film at one point at
the center.

[0072]In an embodiment of the present invention, the SiOCH film is
analyzed via FT-IR and the ratio of strength of Si--CH3 bond and Si--O
bond shown in the spectral waveform is calculated using formula (1) from
the measured values of Si--CH3 peak area and Si--O peak area.

[0074]FIG. 2 shows an example of the spectral waveform of a SiOCH film
before curing, obtained via FT-IR. As shown, the Si--CH3 peak area and
Si--O peak area are calculated.

[0075]Also, the chemical stability of a semiconductor device structure is
known to present no problems in practical applications, from a different
experiment, etc., conducted by the inventors, as long as the decrease in
thickness (ΔThickness) is less than 15 nm and increase in
dielectric constant (Δk) is less than 0.25.

EXAMPLES

Comparative Example

[0076]First, the evaluation result of a comparative example is explained.
A film was formed on a silicon substrate with a diameter of 200 mm using
the plasma CVD apparatus shown in FIG. 1. The film forming conditions
were set as follows:

[0085]The curing time was selected to achieve a k of more than 2.4 but
less than 2.6, and an elastic modulus of more than 8 GPa, after curing.
For your information, the higher the temperature, the greater the effect.
The Si--CH3/Si--O bond strength ratio according to the FI-IR spectrum of
the obtained film, specific dielectric constant (k) after curing, change
(increase) in specific dielectric constant (Δk), film thickness,
change (decrease) in film thickness (ΔThickness), and elastic
modulus, are shown in the top fields of Table 1.

Example

[0086]In the example, the conditions were set based on the following
considerations.

[0087]As the Si--CH3/Si--O bond strength ratio increases, it is assumed
that the percentage of CH3 ends increases relatively at the surface of
the SiOCH film. Accordingly, a relative increase in the percentage of CH3
ends leads to an improvement in the chemical stability with respect to
chemical solutions due to higher hydrophobicity. On the other hand,
increasing the Si--CH3/Si--O bond strength ratio reduces the elastic
modulus.

[0088]Among the parameters that increase the Si--CH3/Si--O bond strength
ratio, changing the film forming conditions/curing conditions in the
following manner are effective:

[0089][1] Lower the susceptor temperature.

[0090][2] Widen the Electrode gap.

[0091][3] Lower the RF power.

[0092][4] Shorten the UV curing time.

[0093]In consideration of the above, the film forming conditions/curing
conditions were set as follows:

[0102]The curing conditions were optimized to achieve a k of more than 2.4
but less than 2.6, and an elastic modulus of more than 8 GPa, after
curing. The Si--CH3/Si--O bond strength ratio according to the FI-IR
spectrum of the obtained film, specific dielectric constant (k) after
curing, change (increase) in specific dielectric constant (Δk),
film thickness, change (decrease) in film thickness (ΔThickness),
and elastic modulus, are shown in FIG. 1 (the film density was approx.
1.2 g/cm3).

[0103]As shown in Table 1, increase in specific dielectric constant
(Δk), and decrease in film thickness (ΔThickness), both
exhibit a high degree of dependence on high Si--CH3/Si--O bond strength
ratio.

[0104]As shown above, by adjusting the Si--CH3/Si--O bond strength ratio
of the SiOCH film to 2.50% or more, the decrease in film thickness
(ΔThickness) becomes less than 15 nm, while the increase in
dielectric constant (Δk) becomes less than 0.25, thereby allowing
the chemical stability of the semiconductor device structure to be
maintained within a range not presenting problems in practical
applications. On the other hand, since the elastic modulus decreases as
the Si--CH3/Si--O bond strength ratio increases, the range of
Si--CH3/Si--O bond strength ratios of the film at which the elastic
modulus also becomes more than 8 GPa is 2.50 to 3.20%. By using films
meeting the above conditions in damascene structures, inter-layer boding
structures can be built without negatively affecting the film
characteristics.

[0105]It will be understood by those of skill in the art that numerous and
various modifications can be made without departing from the spirit of
the present invention. Therefore, it should be clearly understood that
the forms of the present invention are illustrative only and are not
intended to limit the scope of the present invention.